Of all the fears parents face when a child goes out into the world, Amanda Knox's mother and father could never have imagined that just six weeks after their daughter arrived in the quaint, medieval town of Perugia in Italy's Umbrian countryside, she would be in prison.

The 20-year-old is a suspect in the brutal murder of her British roommate, Meredith Kercher, and her family is caught in a nightmare 6,000 miles from their hometown of Seattle.

Curt Knox and Edda Mellas only can see their daughter for an hour twice a week in an Italian prison.

"20/20" traveled to Perugia to investigate the side of story people haven't heard, and Knox's parents and 19-year-old sister, Deanna Knox, are speaking publicly for the first time in an exclusive interview with "20/20" co-anchor Elizabeth Vargas.

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In her prison diary, Knox writes, "I know I am innocent. This is light enough. I may be in prison for a crime I didn't commit, but the truth is out there, and I wait day by day, for it to be discovered. … I am innocent and so I will be free. I will have freedom." (Click here to read a page of Knox's prison diary).

A Dream Becomes a Nightmare

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Knox's parents divorced when she was a toddler, but they raised their two daughters together. They shared the pride when Knox made the Dean's List at the University of Washington, and the financial concerns when she yearned to spend her junior year abroad.

"We basically told her that, you know, here's how much we have available, and she said, 'Well, I can make up the rest,'" said Curt Knox.

According to Deanna Knox, her sister "never went out. She stayed home, studied and worked, and that's all she did, just so she could afford to go [abroad]." Two years, countless jobs and $7,000 later, Knox had made her dream a reality.

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Perugia is an ancient city two hours north of Rome, known mostly today for its chocolates and its universities, which attracts 40,000 student each year from all over the world.

In August 2007, Deanna Knox accompanied her sister on her first visit to Perugia to find a place to live. They settled on a cottage overlooking the Umbrian valley that Knox would eventually share with two Italian women and Kercher, who also came to Perugia from England to fulfill her dream of studying abroad.

Knox's parents say that their daughter and her roommate got along well.

"Everything seemed to be meshing just fine," said Curt Knox. "I got to hear about [how] her and Meredith spent a bunch of time at this big chocolate festival. And she said, 'Yeah, we had the best time.'"

"They got along great," said Mellas.

Some of Kercher's friends say that Knox got too involved in Perugia's lively social scene, that Kercher complained that her roommate partied too much and brought home too many boys. But Deanna Knox says that doesn't sound like her sister.

"I've seen a lot of people at college just lift a lid and just, I'm free, and go nuts. But Amanda definitely didn't do that. … She did not go crazy with men in Italy at any time. I mean, she's a normal girl and she found a guy there, but she did not go crazy."

The guy was Rafaele Sollecito, an Italian engineering student Knox met at a classical music concert.

For Kercher, the experience abroad would take a horrific turn.

On the night of Nov. 1, Kercher went to a friend's house for dinner and then walked home alone. Some time later that night, Kercher was murdered in a brutal assault in her bedroom — her throat was slit, she choked on her blood and she was left partially clothed, covered with a duvet.

Police launched an investigation to find the person responsible for the gruesome murder.

Kercher's family said no one would ever want to kill her. "She was one of the most beautiful, intelligent, witty and caring people that you could wish to meet," said her sister Stephanie Kercher.

An intense investigation ensued, and police theorized that Kercher was killed as an unwilling participant in an extreme drug-fueled sex game.

They quickly focused on Knox and Sollecito. Knox says she returned to her cottage from Sollecito's apartment the next morning to take a shower, but found the front door of the cottage ajar and became suspicious. Concerned, she asked Sollecito to come over and Knox called her mother.

"And she said, 'Well, I was at Rafaele's last night, and I've come home now and I think somebody's been in my house,'" Mellas recalled.

"And she told me, 'We can't find Meredith. We can't get a hold of Meredith. And her room is locked.' And I said, "Hang up and call the police.'"

Police soon arrived at the cottage to return Kercher's cell phones, which were found in a neighbor's yard. After breaking down the door to Kercher's room, police found her dead — her throat slit after an apparent sexual assault.

Police say Knox first told them that she was at Sollecito's apartment the night of the murder. Four days later, she went with Sollecito to police to answer questions and found herself in an overnight interrogation, during which she said she had a vision where she may have been in her apartment when the deadly attack occurred, covering her ears when she may have heard screams. She also thought her employer — bar owner Patrick Lumumba — may have been in Kercher's room that night.

Knox later made a final account that matches her original statement, saying that she slept at Sollecito's apartment that fatal night.

"Her story and her version of what happened that night has totally stayed consistent, absolutely consistent," said Mellas. "If you take out that [overnight] interrogation without a lawyer, without an interpreter, other than that time when she was … like she says, the most scared that she's ever been in her entire life, her story has not changed one iota."

Police felt Knox and Sollecito's changing accounts of the night were enough to arrest them, along with Lumumba, Nov. 6. Just six weeks after arriving to study in Italy, Knox found herself in an Italian jail where suspects can be held for a year without being charged.

Unraveling the Mystery

Immediately after their arrest, the young couple and their behavior during the days after the murder came under fire. The day Kercher's body was discovered, they were videotaped kissing at the crime scene. The following day, they were observed buying what the tabloids described as "lingerie for a night of wild sex."

Police said damning evidence seemed to mount against Knox and Sollecito, including a knife from Sollecito's kitchen that had Knox's DNA on the handle and Kercher's DNA on the blade.

Instantly, Knox was thrown into the center of an international media frenzy.

"This was a horrible crime, but I couldn't understand why immediately Amanda was painted in this horrible light, where she was unrecognizable," said Mellas.

"Amanda is the kindest person I know," Deanna Knox said. "She will do anything to make people happy, and she cares about everyone else before herself."

"20/20" brought in Joe Tacopina, a high-profile New York criminal defense attorney who also has law offices in Italy, to analyze the case, which has been plagued by speculation.

"This case, like many high-profile cases that garner a lot of media attention, is larded with nontruths and rumors that sort of take on a life of their own," he said.

"The prosecution argued that it was a sex game gone wrong, and Patrick Lumumba was involved and Amanda and Raffaele and they all took turns holding her down, while they violated her sexually," he said.

Tacopina was given exclusive access to Italy's top crime lab along with the case files from the prosecution and defense to unravel this mystery.

With three suspects in custody, the prosecutor Giuliano Mignini believed he had found his assailants. But within weeks, Lumumba was released after several people came forward to confirm his alibi and no evidence of him was found at the crime scene.

Police found strong new DNA evidence of another person, Rudy Guede, that didn't match any of their original suspects. However, the prosecutor remained firm in his belief that Knox and Sollecito were involved in Kercher's death, despite their denials of any involvement. He argued that the forensic evidence against the two was still very strong.

Bombshell for the Defense?

Tacopina uncovered records that could be a bombshell for the defense. Records show the DNA match on the knife has less than a 20 percent chance of being connected to Kercher and it is not blood, but rather just a human trace.

"That's not the murder weapon, because if you use that knife as a murder weapon, and as bloody as that crime scene was, you're not going to be able to clean off all the blood, yet leave some other transferable DNA," he said.

Tacopina also says that he learned that additional crime scene photos taken two weeks after the murder showed that "the apartment was rearranged," when compared to the initial crime scene photos.

"The evidence was moved. The bed was leaning up against the wall. … For a crime scene to be worth anything, forensically, it has to be pure and it can't be trampled on, it can't be moved."

Tacopina says this is a "huge blow" to the prosecution's case.

"[There are] countless cases, high profile cases, where the lack of the sanctity of the crime scene has blown the case for the prosecution, starting with O.J. Simpson."

After Lumumba was freed for lack of evidence, prosecutors turned their attention to Guede, who hung out at the basketball court near Kercher and Knox's house. Italy's top forensic lab meticulously matched Guede's palm print to a bloody print on a pillowcase under Kercher's body and identified his DNA inside her.

Guede says he had consensual sexual relations with Kercher the night of her murder. He states that he went to the bathroom and returned to the bedroom to find Kercher alive on the floor with her throat slashed and saw an intruder fleeing the scene. Guede says he put a washcloth on her throat in an attempt to save her, but then left the cottage, fearing for his own life.

"You sort of hear that story and you laugh because it's just so incredible," said Tacopina. "And if true, he is the unluckiest man in the world."

Guede also stated that Knox and Sollecito were not in the cottage that night.

For now, Knox's family waits as investigators slowly sift through the evidence. Mignini insists he has enough to hold the suspects and is sticking with his group sex attack theory.

"You are perceived as guilty if you are put in jail," said Judy Bachrach, a contributing editor for Vanity Fair who has been covering the case from the beginning. "And you are gonna be in jail if you're considered a suspect. And you're gonna be considered a suspect if the prosecutor says you are. Never mind the evidence."

Curiously, Mignini was charged in January, in a separate case, with abusing his office and obstruction of justice, in what an Italian official called a "crusade … to further his own vindictive interest." He has denied the charges.

Myths and Misconceptions

Knox's family won't discuss the case directly, but it has appealed to Italy's supreme court for Knox's release. The hearing is in April.

For now, her parents simply want to clear up what they believe to be myths and misconceptions about their daughter. They countered the criticism of the video shot at the crime scene of Knox and Sollecito kissing.

"She looked like she was in shock," said her father. "I almost saw them as kind of clinging to each other for support, " added her mother.

In response to the caught-on-tape "lingerie moment," Curt Knox points out that "her house is now a crime scene" and Mellas explained that underwear "was one of the first things she needed." Knox's family was also aware of her relationship with Sollecito.

"He looked like Harry Potter, and that's what she liked about him," said Deanna Knox.

They say Knox's MySpace nickname "Foxy Knoxy" was misconstrued in headlines around the world, indicating the fresh-faced college student was a seductress. In reality, Knox got her nickname in soccer when she was 8 years old. Curt Knox said, "She crouches like a fox. She was a defender, and she would set herself, prepare herself to take on the person coming down the field."

From the start, Knox's family has displayed unwavering support and proclaimed her innocence. But public opinion in Italy immediately turned against Knox, who was painted as a sex-crazed, party girl gone wild. Curt Knox says this portrayal is "180 degrees opposite of anything we have ever known her to be."

Twice a week for the last three months, at least one of Knox's parents has visited her in prison.

"Being a young kid, she just doesn't understand — why am I here when I didn't do anything," Curt Knox said.

When they are in the United States, they receive a steady stream of letters from their daughter. Mellas shared one letter: "Dear Mom, it's always so good to see you, amazing, I would say. You are my angel throughout all of this … and you are also most importantly the one person who gives me the most hope."

"It's hard when after so much time the police still think I am involved, it's really hard not being believed, but, you know, I think about you struggling to be OK as well … "

Knox's parents still cling to the belief that eventually their world will make sense again.

"It's one in which you have to believe in the system" said Curt Knox. "And that they wouldn't put an innocent 20-year-old girl in jail for something she didn't do," said Mellas. "You just have to believe that."